Frequency control of highfrequency oscillations



Nov. 14, 1950 l.. E. THOMPSON FREQUENCY CONTROL OF HIGH-FREQUENCY OSCILLATIONS 2 Sheets-Sheet 1 Original Filed Feb. 6, 1945 INVENTOR N w P Y M E O l. N H R T o T D N/ Y B LELA SWU NES@ XENQ N msN Nov. 14, 1950 E. THOMPSON FREQUENCY CONTROL OF' HIGH-FREQUENCY OSCILLATIONS 2 Sheets-Sheet 2 Original Filed Feb. 6, 1945 INVENTOR LEI-.AND E. THOMPSON low-wk.

ATTORNEY Patented Nov. 14, 1950 UNITED `STATES PATENT OFFICE FREQUENCY CONTROL OF HIGH- FREQUENCY OSCILLATIONS Leland E. Thompson, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Serial No. 5,013

4 Claims.

This is a division of my co-pending application Serial Number 576,453, led February 6, 1945, Patent No. 2,514,425, entitled Radio Relayng. This application is also a division of my application Serial Number 654,553, led March 15, 1946, Patent No. 2,47 6,162.

In my co-pending parent application referred to, l have described an ultra short wave radio relaying system making use of an ultra short wave oscillation generator. This oscillation generator is of the type making use of a cavity resonator having a gap, oscillations being produced in the resonator by an electron discharge system including a negatively charged anode, a positively charged grid and a cathode.

The object of my present invention is to provide circuits for automatically frequency controlling this type of oscillator, particularly when employed as a heterodyning oscillator. Other objects, advantages and features will appear with the more detailed description of my present invention.

In the drawings, Fig. 1 is a block diagram of a radio relay station as described in my parent application, and Fig. 2 illustrates certain circuit details of Fig. 1.

Referring to Fig. 1 in general terms, the received waves (which are doubly frequency modulated at the remote transmitter, not shown) are converted to a suitable intermediate frequency, amplified, and then subjected to a single frequency demodulation. The Waves resulting from this single frequency demodulation are then used in part for purposes of automatic frequency control of the local beating oscillator and to frequency modulate a new locally generated carrier. The waves received by Fig. 1 may, for example, emanate from a transmitter wherein a carrier having a mean frequency of 3000 megacycles is frequency modulated plus and minus 1.0 megacycle for maximum deviation.

More specifically referring to Fig. 1, the waves are picked up or received on a receiving antenna RAZUD. The received waves are beat down in frequency in a converter circuit 202 with waves from a local beating oscillator 204. The intermediate frequency produced may be 30 megacycles plus and minus 1.0 megacycle. The Waves of intermediate frequency are amplified in an intermediate frequency amplifier 206 and then fed to a discriminator detector 208.

The action of the discriminator detector is such as to produce a wave of one megacycle plus and minusV kilocycles as explained in my parent application. This wave is limited and amplified in appropriate apparatus 2H) andthen used to frequency modulate oscillator 2|2 Whose unmodulated frequency may be 3010 megacycles.

As indicated in Fig. 1 the service channel band may be ltered out by filter SCF and taken from line SCL for use in earphones, or the output of line SCL may be fed by patch cords to the service line input SLI to modulate oscillator 2|2.

By adjusting the amplitude of the output of amplifier 2li) the waves radiated over the transmitting antenna TA2I4 of the relay point of Fig. 1 may be made 3010 megacycles plus and minus 1.0 megacycle.

All values of frequencies, resistances, voltages, etc. are given as illustrative or typical only and, therefore, it is to be clearly understood that all inventions described herein with reference to all gures of the drawings are not to be restricted to such values. y

Fig. 2` illustrates in greater detail the beating oscillator-converter apparatus designated schematically at 202 and 204 in Fig. 1. That is, the receiving antenna RA200 of Fig. 1 is connected to the transmission line 100 of Fig. 2. Line 100 is provided with an external metallic shield 102,

grounded at 104. Also, transmission line 100 is terminated by an inductive vloop 105, thereby establishing coupling within the re-entrant type cavity resonator 106. If desired, transmission line 100, 102 may be replaced by a wave chute or guide.

The cavity resonator 106 is of metal and cylindrical in shape. Extending within the resonator 106 and connected to one of its bases is cylindrical line section 190 whose base 19| is adjacent and spaced from the metal circular base 192 carried by metal bellows 1I l. The line section 190 is tuned by means of this cylindrical metallic bellows 1H having, as indicated, springy corrugated side walls. By means of the bolt 1l3 and nut 1|5, the capacity between plates 19| and 192 is adjusted as is also the volume or internal cubical content of the resonator. Preferably the line section 190 is approximately one-'quarter wavelength long-here about 1%, of one inch. This line section is tuned by adjustment of plate 192 to the frequency of the waves received and fed in at 105. A crystal detector 108 is mounted as shown with one terminal 195 in electrical contact with metallic wall 106 and its other terminal 196 protruding through opening 191 in the cylindrical line section 190. Terminal 196 is connected to conductor or line 110. As a result, the crystal detector rectiiies the waves fed in by probes 105 and 1l8 and feeds the resulting difference frequency of about 30 mc. into line 110.

The cavity resonator 106 is also supplied with high frequency oscillations by means of a capacity end plate 1|8 fixed to an exposed section of transmission line 120 protruding within the resonator. The line 120 is excited by an automatically frequency controlled high frequency oscillator operating in the neighborhood of either 3030 megacycles or 2070 megacycles. The oscillator will be described more fully later.

The beat frequency is fed through line 110 shielded by the external conductor 'H2 to the primary 1l6 of a transformer 800 whose secondary coil 126 is tuned by condenser 128. The output of the tuned circuit 126, 128 is fed through line 132 to the first stage of the intermediate frequency amplifiers and limiters 206 of Fig. 1.

In Fig. 2 the oscillator comprises an evacuated container 138, a cathode 134 grounded at 136, a negatively biased plate 156, a positively charged cavity resonator 142 and a grid 144 connected to the resonator. The resonator 142, shown in cross section, is cylindrical in shape and is made of metal. The resonator has metallic bases 152, 154 which are perforated and to which are attached the hollow metallic tubes 146, 150. The tubes 146, 150 are separated at an intermediate point so as to provide a gap 148. As explained in my parent application, oscillations are set up in the cavity resonator 142 of Fig. 2 and wave output is derived from the inductive loop 140 coupled to the space within the cavity resonator 142.

The external surface of the cavity resonator` 106 is grounded at 104 as indicated.

By properly choosing the dimensions of the cavity resonator 142 and by appropriate adjustment of the voltages on the elements of the oscillator, oscillation at a desired frequency may be had. By suitable external means the shape of resonator 142 may be warped so as to change its cubcal content and, hence, its frequency of operation. Or, if desired, a metallic bellows adjustment, such as that provided for the cavity resonator 106 may be provided for 142, but in this case, of course, the container 138 should be hermetically sealed to resonator 142 so that a portion of its external surface containing and otherwise supporting the metallic bellows structure would be exposed for external adjustment.

The output appearing in the tuned circuit 126, 128 would be, for the example chosen, a Wave as indicated in Fig. 1 having a mean frequency of 30 megacycles and maximum frequency deviation of $1.0 megacycle. This wave is fed to the intermediate frequency amplifying, limiting and discriminating detector stages.

The discriminator detector of Fig. 1 is also diagrammatically illustrated at 208 in Fig. 2 across the output terminals of which are connected resistors 182, 184, which provide automatic frequency controlling voltages. These voltages may then be used to control the frequency of oscillator 138 so as to maintain the beat frequency waves within the pass band of intermediate frequency amplifying and limiting stages 206 of Fig. 1.

The frequency controlling circuit for the oscillator 138, from which the automatic frequency controlling voltages are derived, is illustrated schematically in Fig. 2 in connection with vacuum tube 160. More specifically, a source of voltage 165 is connected across the leads or terminals 116, 118 and these terminals are connected to a potentiometer 114. By properly adjusting the tap 112 on potentiometer 114, and by proper choice of values for other circuit elements, the current flow through, or the conductivity of tube 160, having the anode 162, grid 164, and the cathode 168, may be controlled so that the voltage applied through lead 158 upon the plate 156 is of a desired value, such as, for example, volts. As indicated, the plate circuit for tube 160 is returned to ground through a resistor 16| shunted by condenser 192a and through the ground connection 163 to the source of potentials 165. It should, therefore, be clear that the automatic frequency controlling voltages appearing across resistors 182 and 184 will vary the current flow through the tube 160 and hence its effective resistance. Consequently, the voltage in lead 158 will vary in such a way as to control the oscillator in that direction which will bring the beat frequencies appearing in 126, 128 back to the desired intermediate frequency pass band of the IFA system 206 of Fig. 1.

What is claimed is:

1. A control circuit for an oscillation generator, said oscillation generator comprising a container containing an electron emitting cathode and an anode, a cavity resonator having a gap, means including one or more sources of unidirectional potential for maintaining said resonator at a positive potential with respect to said cathode and said anode at a negative potential with respect to said cathode, said control circuit comprising a vacuum tube havinfr a plate conductively connected to the anode of said oscillator, and having a grid, and a cathode, a circuit including a source of potential of said aforesaid means extending from said last cathode to the cathode of said oscillator so arranged as to maintain a negative voltage on the plate of said vacuum tube with respect to the cathode of the oscillation generator, and a circuit for applying controlling voltages to the grid of said vacuum tube to vary the conductivity thereof.

2. Apparatus as claimed in claim l, characterized by the fact that a resistance is connected between the plate of said vacuum tube and the cathode of said oscillation generator.

3. A control circuit for an oscillation generator, said oscillation generator comprising a container containing an electron emitting cathode and anode, a cavity resonator having a gap, said resonator being maintained at a positive potential with respect to said cathode and said anode being maintained at a negative potential with respect to saidl cathode, said control circuit comprising a vacuum tube having a plate conductively connected to the anode of said oscillator, said vacuum tube also having a grid and a cathode, a source of unidirectional potential having a potentiometel` connected across its terminals, a tap on said potentiometer connected to the cathode of said vacuum tube, connections capable of passing direct current extending from the cathode of said generator and from said source to a point of reference potential, said tap being .so chosen and said connections so arranged that the plate of said vacuum tube is continuously maintained at a negative D. C. potential REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 'Iunick Dec. 21, 1943 Dow July 23, 1946 Snow Oct. 8, 1946 Morton Oct. 15, 1946 North Dec. 24, 1946 Varian et ai. Jan. 21, 1947 vTomlin June 29, 1948 

